In semiconductor packaging technology, the process of building contact bumps on I/O pads of an integrated circuit chip is very important. It allows the chip to communicate with a circuit board on a substrate on which it is mounted. Since contact bumps are frequently constructed by complex vacuum processing and elaborate multilayer structure of the I/O pads, the bumps contribute to a large portion of the total packaging cost. For chips, the multilayer pad structure is called ball limiting metallurgy (BLM) and, the bumps are made by the well known controlled collapsed chip connection (C4) process. A fabrication process for building bumps and for the subsequent bonding of the bumps to a chip which can be accurately controlled with high reliability and for high I/O counts not achievable by other manufacturing methods is therefore very desirable.
In a conventional method of building contact bumps, bumps of a lead (Pb)-rich alloy are deposited on aluminum pads positioned on the surface of an integrated circuit (IC) chip. In a more recently developed packaging technology for area array chips, the chips are first bumped with an alloy containing lead and then tested by using a test head equipped with sharp pins. The Pb-containing solder bumps which are relatively soft are damaged during the test which then requires an additional reflow process prior to the chip joining step.
The chip testing (or burn-in) for functional and reliability such as a known-good-die (KGD) test is an important and necessary step in IC chip fabrication and therefore, it is very desirable to provide an IC package that can be tested without suffering damage. This becomes more important when inexpensive chips are mounted on expensive substrates. It is also desirable to build bumps on the I/O pads of IC chips with a reworkable material such that the IC chip can be debonded from a substrate (or another IC chip) if defects are found during testing or operation in the field. In general, a desirable contact bump should also be mechanically compliant, elastic and has low contact resistance. A desirable contact bump should also be stable under various environmental conditions such as heat and humidity that are frequently encountered in service environments.
It is therefore an object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive bumps adhered to the pads that does not have the drawbacks and shortcomings of conventional electronic devices equipped with pads and bumps.
It is another object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive bumps adhered to the pads such that the bumps are reworkable after being bonded to a substrate or another electronic device. Multilayer ceramic or organic circuit board are examples of substrates conventionally used.
It is a further object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive composite bumps adhered to the pads wherein the bumps are formed of a material consisting of thermoplastic polymeric binder and at least about 30% by volume of a conductive metal particles based on the total volume of the metal particles and the thermoplastic polymer.
It is still another object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive composite bumps adhered to the pads wherein the composite bumps are compliant and elastic to allow the bumps to establish electrical interconnection with another electronic device by the application of a compressive force on the devices.
It is yet another object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive composite bumps adhered to the pads wherein the composite bumps are compliant and pliable when compared to conventional solder bumps such that highly reliable interconnections to another electronic device can be made.
It is another further object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive composite bumps adhered to the pads such that the electronic device can be interconnected to another electronic device that is similarly equipped with pads and composite bumps by mechanical means.
It is still another further object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive composite bumps adhered to the pads such that the electronic device can be interconnected electrically to another electronic device that is similarly equipped with pads and composite bumps under a predetermined pressure and heat.
It is yet another further object of the present invention to provide an electronic device that is equipped with a plurality of pads and electrically conductive composite bumps adhered to the pads such that after the device is bonded to another electronic device similarly equipped with composite bumps, the two electronic devices can be separated by reworking the composite bumps under heat and solvent.
It is yet another further object of the present invention to provide a method of fabricating an electronic device that is equipped with a plurality of pads and electrically conductive composite bumps adhered to the pads wherein the composite bumps are formed by a thermoplastic polymeric binder and at least about 30% by volume of conductive metal particles based on the total volume of the metal particles and the thermoplastic polymer.